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Nontranscriptional modulation of intracellular Ca2+ signaling by ligand stimulated thyroid hormone receptor.

Saelim N, John LM, Wu J, Park JS, Bai Y, Camacho P, Lechleiter JD - J. Cell Biol. (2004)

Bottom Line: Coexpression of TRbetaA1 with retinoid X receptor did not enhance regulation.Both xTRbetaA1 and the homologous shortened form of rat TRalpha1 (rTRalphaDeltaF1) localized to the mitochondria and increased O2 consumption, whereas the full-length rat TRalpha1 did neither.We conclude that T3-bound mitochondrial targeted TRs acutely modulate IP3-mediated Ca2+ signaling by increasing mitochondrial metabolism independently of transcriptional activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, 78229, USA.

ABSTRACT
Thyroid hormone 3,5,3'-tri-iodothyronine (T3) binds and activates thyroid hormone receptors (TRs). Here, we present evidence for a nontranscriptional regulation of Ca2+ signaling by T3-bound TRs. Treatment of Xenopus thyroid hormone receptor beta subtype A1 (xTRbetaA1) expressing oocytes with T3 for 10 min increased inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ wave periodicity. Coexpression of TRbetaA1 with retinoid X receptor did not enhance regulation. Deletion of the DNA binding domain and the nuclear localization signal of the TRbetaA1 eliminated transcriptional activity but did not affect the ability to regulate Ca2+ signaling. T3-bound TRbetaA1 regulation of Ca2+ signaling could be inhibited by ruthenium red treatment, suggesting that mitochondrial Ca2+ uptake was required for the mechanism of action. Both xTRbetaA1 and the homologous shortened form of rat TRalpha1 (rTRalphaDeltaF1) localized to the mitochondria and increased O2 consumption, whereas the full-length rat TRalpha1 did neither. Furthermore, only T3-bound xTRbetaA1 and rTRalphaDeltaF1 affected Ca2+ wave activity. We conclude that T3-bound mitochondrial targeted TRs acutely modulate IP3-mediated Ca2+ signaling by increasing mitochondrial metabolism independently of transcriptional activity.

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The truncated rTRα1ΔF regulates intracellular Ca2+ release. (a) Spatio-temporal stacks of IP3-induced Ca2+ wave activity in control oocytes compared with oocytes expressing rTRα1ΔF or rTRα1ΔF. TR expressing oocytes were treated with 100 nM T3 10–15 min before IP3 (∼300 nM) injections and confocal imaging. (b) Western blots of rTRα1 and rTRα1ΔF expression levels in experimental oocytes. (c) Histogram of the average interwave periods for each group (n values in parentheses). Note that rTRα1ΔF has significantly longer periods even though its expression levels are lower than those of full-length rTRα1. The asterisks (**) indicate statistical significance with P < 0.01 using ANOVA single factor.
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fig10: The truncated rTRα1ΔF regulates intracellular Ca2+ release. (a) Spatio-temporal stacks of IP3-induced Ca2+ wave activity in control oocytes compared with oocytes expressing rTRα1ΔF or rTRα1ΔF. TR expressing oocytes were treated with 100 nM T3 10–15 min before IP3 (∼300 nM) injections and confocal imaging. (b) Western blots of rTRα1 and rTRα1ΔF expression levels in experimental oocytes. (c) Histogram of the average interwave periods for each group (n values in parentheses). Note that rTRα1ΔF has significantly longer periods even though its expression levels are lower than those of full-length rTRα1. The asterisks (**) indicate statistical significance with P < 0.01 using ANOVA single factor.

Mentions: Finally, we tested whether targeting of TRs to mitochondria was required to regulate Ca2+ signaling. As before, oocytes were injected with either full-length rTRα1 or NH2 terminus–truncated rTRα1ΔF mRNAs. Protein expression levels were measured 2–3 d after injection (Fig. 10 b). Ca2+ activity was confocally imaged 10 min after treatment with T3 (100 nM). We found that the average Ca2+ interwave period for rTRα1ΔF-injected oocytes was 8.8 ± 0.26 s (n = 24), which was significantly higher (ANOVA single factor, P < 0.01) than full-length rTRα1-expressing oocytes (7.9 ± 0.38 s, n = 22) and the water-injected control group (7.2 ± 0.24 s; n = 30; Fig. 10, a and c). Together, these data strongly indicate that the regulation of Ca2+ signaling by T3-activated TRs requires their localization within mitochondria.


Nontranscriptional modulation of intracellular Ca2+ signaling by ligand stimulated thyroid hormone receptor.

Saelim N, John LM, Wu J, Park JS, Bai Y, Camacho P, Lechleiter JD - J. Cell Biol. (2004)

The truncated rTRα1ΔF regulates intracellular Ca2+ release. (a) Spatio-temporal stacks of IP3-induced Ca2+ wave activity in control oocytes compared with oocytes expressing rTRα1ΔF or rTRα1ΔF. TR expressing oocytes were treated with 100 nM T3 10–15 min before IP3 (∼300 nM) injections and confocal imaging. (b) Western blots of rTRα1 and rTRα1ΔF expression levels in experimental oocytes. (c) Histogram of the average interwave periods for each group (n values in parentheses). Note that rTRα1ΔF has significantly longer periods even though its expression levels are lower than those of full-length rTRα1. The asterisks (**) indicate statistical significance with P < 0.01 using ANOVA single factor.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2172460&req=5

fig10: The truncated rTRα1ΔF regulates intracellular Ca2+ release. (a) Spatio-temporal stacks of IP3-induced Ca2+ wave activity in control oocytes compared with oocytes expressing rTRα1ΔF or rTRα1ΔF. TR expressing oocytes were treated with 100 nM T3 10–15 min before IP3 (∼300 nM) injections and confocal imaging. (b) Western blots of rTRα1 and rTRα1ΔF expression levels in experimental oocytes. (c) Histogram of the average interwave periods for each group (n values in parentheses). Note that rTRα1ΔF has significantly longer periods even though its expression levels are lower than those of full-length rTRα1. The asterisks (**) indicate statistical significance with P < 0.01 using ANOVA single factor.
Mentions: Finally, we tested whether targeting of TRs to mitochondria was required to regulate Ca2+ signaling. As before, oocytes were injected with either full-length rTRα1 or NH2 terminus–truncated rTRα1ΔF mRNAs. Protein expression levels were measured 2–3 d after injection (Fig. 10 b). Ca2+ activity was confocally imaged 10 min after treatment with T3 (100 nM). We found that the average Ca2+ interwave period for rTRα1ΔF-injected oocytes was 8.8 ± 0.26 s (n = 24), which was significantly higher (ANOVA single factor, P < 0.01) than full-length rTRα1-expressing oocytes (7.9 ± 0.38 s, n = 22) and the water-injected control group (7.2 ± 0.24 s; n = 30; Fig. 10, a and c). Together, these data strongly indicate that the regulation of Ca2+ signaling by T3-activated TRs requires their localization within mitochondria.

Bottom Line: Coexpression of TRbetaA1 with retinoid X receptor did not enhance regulation.Both xTRbetaA1 and the homologous shortened form of rat TRalpha1 (rTRalphaDeltaF1) localized to the mitochondria and increased O2 consumption, whereas the full-length rat TRalpha1 did neither.We conclude that T3-bound mitochondrial targeted TRs acutely modulate IP3-mediated Ca2+ signaling by increasing mitochondrial metabolism independently of transcriptional activity.

View Article: PubMed Central - PubMed

Affiliation: Department of Cellular and Structural Biology, University of Texas Health Science Center at San Antonio, 78229, USA.

ABSTRACT
Thyroid hormone 3,5,3'-tri-iodothyronine (T3) binds and activates thyroid hormone receptors (TRs). Here, we present evidence for a nontranscriptional regulation of Ca2+ signaling by T3-bound TRs. Treatment of Xenopus thyroid hormone receptor beta subtype A1 (xTRbetaA1) expressing oocytes with T3 for 10 min increased inositol 1,4,5-trisphosphate (IP3)-mediated Ca2+ wave periodicity. Coexpression of TRbetaA1 with retinoid X receptor did not enhance regulation. Deletion of the DNA binding domain and the nuclear localization signal of the TRbetaA1 eliminated transcriptional activity but did not affect the ability to regulate Ca2+ signaling. T3-bound TRbetaA1 regulation of Ca2+ signaling could be inhibited by ruthenium red treatment, suggesting that mitochondrial Ca2+ uptake was required for the mechanism of action. Both xTRbetaA1 and the homologous shortened form of rat TRalpha1 (rTRalphaDeltaF1) localized to the mitochondria and increased O2 consumption, whereas the full-length rat TRalpha1 did neither. Furthermore, only T3-bound xTRbetaA1 and rTRalphaDeltaF1 affected Ca2+ wave activity. We conclude that T3-bound mitochondrial targeted TRs acutely modulate IP3-mediated Ca2+ signaling by increasing mitochondrial metabolism independently of transcriptional activity.

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